The era of contention among various principalities on the Iberian
Peninsula was an incubator of constitutional thought. As Christian
and Moorish nations fought, formed and reformed, rose and fell,
princes had to make some accommodations to the various players whose
support they needed. Some of this took the form of documents of a
constitutional character, many of which had an influence that
reached to other nations.

Fuero Juzgo, Wikipedia. In 1348, the Ordenamiento de Alcalá granted it legal preeminence over the Siete Partidas. The Fuero Juzgo reigned until the creation of the Spanish Civil Code near the end of the nineteenth century. Presently, it retains some legal force with respect to certain auxiliary civil fueros in the Basque Country, Navarra, and Aragon.